How Good Are Those Young-Earth Arguments?
A Close Look at Dr. Hovind's List of Young-Earth Arguments and Other Claims
by Dave E. Matson
Copyright © 1994-2002
Young-earth "proof" #12: The volume of lava on earth divided by its rate of efflux yields only a few million years. The earth is not billions of years old.
Presently, when mountain ranges are being actively built up, the output of magma is almost certainly much higher than usual. There may have been long, quiet periods when little happened in the way of mountain building and volcanic activity. Enormous amounts of crust have been recycled in the subduction of oceanic plates. Enormous amounts of continental crust have been eroded away, only to be recycled. Morris has not addressed these and other problems.
Morris and Parker  list an age of 500 million years based on the "influx of magma from mantle to form crust." This calculation, which appears in Morris , is based on the volume (0.2 cubic km/yr) of lava erupted by Paricutin Volcano in Mexico during the 1940s. Morris  notes that intrusive rocks are much more common than lava flows:
... .so that it seems reasonable to assume that at least 10 cubic kilometers of new igneous rocks are formed each year by flows from the earth's mantle.
The total volume of the earth's crust is about 5 x 109 cubic kilometers. Thus, the entire crust could have been formed by volcanic activity at present rates in only 500 million years, which would only take us back into the Cambrian period. ... The uniformitarian model once again leads to a serious problem and contradiction. [Morris, 1974, p.157]
But the "uniformitarian model" of which Morris  is so critical is a product of Morris , not science. He has pulled the value of 10 km3/yr from thin air, assumed that this fictitious rate has been constant over time, and neglected erosion, sedimentation, crustal recycling, and the fact that the injection of magma into the crust is a highly nonuniform process about which little is known. Morris' (92) calculation is worthless.
(Dalrymple, 1984, p.111)
Thus, another young-earth argument bites the dust due to the use of a dubious rate. It's not good enough to find some rate; one must show that it is sound.